Tunnel driving apparatus

ABSTRACT

An advanceable shield for a tunnel driving apparatus which is composed of a series of elongate members arranged side-by-side and supported on relatively movable frames to define an internal excavating space. The members are selectively connectible with the frames and can be advanced by relative displacement between the frames. Some of the members, preferably over the floor region of the shield, are each of multi-part construction with a main elongate hollow body and a U-shaped hollow component pivotably connected thereto and receivable therein. Means, such as a piston and cylinder unit is provided to move the component in relation to main body so as to expand or contract a dimension at the rear end of the member to thereby permit the member to tilt about an axis extending transversally of the longitudinal axis of the tunnel. In this way control of the direction of advancement of the tunnel can be effected.

United States Patent 1 1 Foik Dec. 16, 1975 l TUNNEL DRIVING APPARATUS Inventor: Adolf Foik, Altlunen, Germany [73] Assignec: Gewerkschaft Eisenhutte Westfalia,

Westphalia, Germany [22] Filed: July 2, 1974 [21] Appl. No: 485,303

Primary E.\'umincrlacob Shapiro Attorney, Agent, or FirmTh0mpson Birch, Gauthier & Samuels [57] ABSTRACT An advanceable shield for a tunnel driving apparatus which is composed of a series of elongate members arranged side-by-side and supported on relatively movable frames to define an internal excavating space. The members are selectively connectiblc with the frames and can be advanced by relative displacement between the frames. Some of the members, preferably over the floor region of the shield. are each of multipart construction with a main elongate hollow body and a U-shaped hollow component pivotably con nected thereto and receivable therein. Means, such as a piston and cylinder unit is provided to move the component in relation to main body so as to expand or contract a dimension at the rear end of the member to thereby permit the member to tilt about an axis extending transversally of the longitudinal axis of the tunnel. In this way control of the direction of advancement of the tunnel can be effected.

24 Claims, 5 Drawing Figures US. Patent Dec. 16, 1975 Sheet10f2 3,926,005

U.S. Patent Dec. 16, 1975 Sheet 2 of 2 3,926,005

I; E Q

Ml IQ TUNNEL DRIVING APPARATUS BACKGROUND TO THE INVENTION The present invention relates in general to tunnel driving apparatus and more particularly to advanceable cutting or support shields for use in tunnel driving operations.

In the driving of tunnels, galleries and similar underground excavations it is well known to use a shield which contacts the wall (which term includes the floor) of the tunnel and defines an excavation space through which material can be removed as the tunnel progresses. The shield supports the tunnel wall and protects the other anciliary equipment which works within the excavation space. It is also known to construct the shield from a series of elongate members, commonly referred to as planks, which are arranged side-by-side and extend with their longitudinal axes more or less parallel to the axis of the tunnel. In order to advance the shield as the tunnel progresses various arrangements are known to advance the members individually or in groups and the rear portion of the tunnel wall behind the members can be supported by lining sections either permanently or temporarily. One arrangement for advancing the members consists of frames supporting the members and hydraulic rams for displacing one frame along the tunnel relative to the other. The members either individually or in groups can then be selectively locked to one or other of the frames. In such an operation it has hitherto been difficult to control the direction of the tunnel advancement since the shield is apt to drift out of alignment with the desired direction and usually the shield drifts towards the floor of the tunnel. To compensate for this mis-alignment it has been known to advance all the members at the roof of the tunnel together to thereby attempt to urge the rear ends of the members at the floor region towards the floor so that these members tend to rise. Such action is only possible where the nature of the material of the tunnel is suitable and in practice the shield is subjected to extremely high forces during such an operation. Moreover there can be no proper control of the advancement direction since this measure merely. attempts to compensate for the tendency of the shield to drift towards the floor.

A general object of this invention is to provide an improved shield permitting control of the tunnel advancement which avoids these disadvantages.

A further object of the invention is to provide an improved elongate member for such a shield, which member is particularly but not solely intended for use over the floor region of the shield and which permits the aforementioned control.

SUMMARY OF THE INVENTION In one aspect the invention provides a multi-part elongate member for a shield which member is composed of a main body, a further component connected to the main body and means for selectively displacing the further component generally transversally of the longitudinal axis of the main body.

Preferably the further component is pivotably connected to the main body and the displacing means effects pivotal movement of the further component outwardly or inwardly in relation to a plane containing an external surface of the main body. By arranging a plurality of these multipart members over the floor region of the shield control can be effected by operating the displacing means of the members to pivot the further components thereof in relation to the floor of the tunnel wall to permit each of the members to tilt about an axis at the tunnel wall extending transversally of the longitudinal axis of the tunnel.

In known manner each member can have a cutting portion at its front end. The displacing or pivoting means for each multi-part member can be in the form of a piston and cylinder unit. By operating the members to provide clearance between a floor-engaging part of the further components thereof the front ends of the main bodies of the members can be made to lift away from the floor to counteract any tendency for the shield to drift towards the floor during advancement. This rising of the front ends of the main bodies of the multipart members will occur automatically once the aforementioned clearances have been established mainly due to the weight of the shield but also due to the relative forces which occur during displacement of the members. The multi-part members can also be arranged in regions other than the floor region of the shield to provide control in other directions. The control of the tunnel advancement direction can be achieved without excessive loading of the shield or its components. In practice a construction is preferred in which the main body of each multi-part member has a rear portion which is generally of U-shaped cross-section open to the floor or wall of the tunnel with the further component being similarly shaped and receivable within the rear portion of the main body. The main body may have a front portion with a bottom wall which contacts the floor or wall and the further component may have a similar bottom wall which can be made co-planar with the bottom wall of the front portion of the main body or moved inwardly thereof to establish the aforementioned clearance.

The rear portion of the main body and the further component preferably have tapered side walls which decrease in width towards the rear end of the member. The further component is preferably connected to the associated main body with pivot pins extending inwardly of the member and lying somewhat forwardly of the centre of the member. Conveniently the front end portion of the main body has side walls continuous with the side walls of the rear end portion and the latter side walls terminate in shoulders at the side walls of the front end portion. These shoulders may then adjoin a terminal end of the bottom wall of the front end portion to form a support surface about which the tilting of the member may occur.

The invention may be understood more readily and various other features of the invention may become more apparent from consideration of the following description.

BRIEF DESCRIPTION OF DRAWINGS An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, wherein:

FIG. 1 is a side view of a member for a support shield made in accordance with the invention;

FIG. 2 is a sectional plan view of the member shown in FIG. 1;

FIG. 3 is a side view of a rear end part of the member shown in FIG. 1 but depicting a different operating position to that depicted in FIG. 1;

FIG. 4 is a diagrammatic side view of a support shield employing members as depicted in FIGS. 1 to 3; and

FIG. is a diagrammatic cross-sectional view of the shield shown in FIG. 4.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring initially to FIGS. 4 and 5 a support or cutting shield for use in driving tunnels is composed of a number of individual elongate members or planks, M, M arranged side by side to define an excavating space Q. Each member M, M has a cutting portion 11 at its forward end. In known manner the members M engage on and support the tunnel wall over the sides and roof, while the members M rest on the floor 19 of the tunnel. The members M are each of integral unitary structure known per se whereas the members M are of multi-part construction as described hereinafter. Two frames 30, 31 are spaced along the shield and have a configuration generally matching the cross-section of the excavating space Q. These frames 30, 31 support the members M, M and operate in combination to effect selective advancement of the members M, M longitudinally of the tunnel. To this end, double-acting hydraulic rams 32 are connected between the frames 31 and can be operated to effect relative movement between the frames 30, 31 and in the longitudinal direction of the tunnel. Each member M, M can be detachably secured-to either or both of the frames 30, 31 and means, such as locking pins insertable into bores in the frames 30, 31 and the members M, M can be provided for this purpose. To advance any one of the members M, M the member M, M in question is secured or locked to the frame 31, e.g., with the locking pin or pins, while the remaining members M, M to be advanced is detached from the frame 30 while the remaining members M, M are all secured to the frame 30.

The rams 32 are now subjected to pressure fluid to urge the frame 31 and the member M, M connected thereto forwardly in the direction of arrow P in FIG. 4. The frame 30 acts as an abutment since it is effectively held in frictional engagement with the tunnel wall with the aid of the member M, M connected therewith. When the member M, M connected to the frame 31 has been advanced sufficiently possibly by the full stroke of the rams 32 the member M, M is disengaged from the frame 31 and the rams 32 are operated in the reverse sense to return the frame 3 l to its former position. Another member M, M can then be connected to the frame 31 and advanced as before and this process can be repeated. When a sufficient number of members M, M have been advanced the frame 31 can become the abutment for the frame 30 which is then used to draw up the rest of the members M, M in succession. Instead of advancing the members M, M individually, groups of members M, M can be advanced by connecting these members-M, M to the frame 30, 31 as the case may be.

The construction of the special members M will now be described with reference to FIGS. 1 to 3. The special multi-part elongate member depicted in FIGS. 1 to 3 has a main body which is formed at its front end with a tapered cutting portion 1 1. At the rear end the body 10 has lugs forming a bracket 12 which receives a pin which in turn is pivotably connected to the cylinder of a small piston and cylinder unit 13. The body 10 is itself composed of two parallel side walls 15, 16 which extend substantially over the entire length of the member and a bottom wall 17 connected between the side walls 15, 16 and extending from the cutting portion 11 to terminate somewhat less than half way along the length of the member. The walls 15, 16, 17 can be conveniently interconnected by welding and additional webs or bars 20 which extend parallel to the side walls 15, 16 are welded into the structure to provide reinforcement. The webs 20 only extend over approximately the length of the bottom wall 17. At the rear terminal end of the wall 17, the side walls 15, 16 are each cut away at the bottom edge to form a tapered recess with a shoulder 18 at the forward end and a bottom edge 15, 16'. These edges 15', 16 taper gradually towards the rear end of the member so the height of the side walls 15, 16 decreases towards the rear end of the member. As depicted in FIG. 1, the member is used in such a disposition that the tapered recesses directly face the tunnel wall or floor denoted 19. A top wall 21, which lies inwardly from the tunnel wall or floor 19 during use, extends between the side walls 15, 16 and extends parallel to the bottom wall 17. In contrast to the bottom wall 17 the top wall 21 extends over substantially the entire length of the member. The front end portion of the body 10 extending up to the shoulders 18 is thus formed with a rigid box-section profile defined by the walls 15, 16, 17, 21 whereas the rear end portion of the body 10 extending from the shoulders 18 is formed as a U-section profile open towards the tunnel wall or floor 19. The rear end portion of the body 10 has reinforcing webs 20 attached as by welding to the top wall 21 thereof and extending parallel to the webs 20 and substantially over the entire length of this rear end portion.

A separate component 22 of the member which is movable transversally in relation to the longitudinal axis of the body 10 thus described is also of U-shaped configuration with a bottom wall 24, which, during use, faces the tunnel wall or floor 19, adjoining side walls 25, 25

The side walls 25, 25 also taper towards the rear of the member as shown in FIG. 1 and have holes which receive pivot pins 23 which can be conveniently welded into holes in the side walls l5, 16 of the main body 10 to extend inwardly thereof. Reinforcement webs 26 which extend parallel and closely adjacent the webs 20 are attached as by welding to the bottom wall 24 and lie inwardly of the webs 20' in relation to the longitudinal axis of the member. The webs 26 extend over substantially the same length as the webs 20 and the webs 20, 26 in common have holes which receive the pivot pins 23. The component 22 composed of the parts 24, 25, 25 26 can thus be pivoted on the pins 23 in relation to the main body 10 and to effect this pivotal movement the rear end of the component 22 is connected to the piston rod 14 of the unit 23. During use the unit 13 can be operated to extend the piston rod 14 and thereby to swing the component 22 outwardly so that the wall 24 is urged against the wall or floor 19 of the tunnel and in general the walls 17, 24 are then coplanar. In this position because of the tapering of the walls 15, 16, 25, 25 a tapered gap 27 is present between the lower end 15', 16 of the walls 15, 16 and the upper edge of the walls 25, 25 respectively. The unit 13 can also be retracted so that the component 22 swings inwardly of the main body 10 and in the direction of arrow S in FIG. 3. In this position a tapered gap 28 is present between the tunnel wall or floor 19 and the wall 24 and hence the entire member can be tilted about a support fulcrum 29 at the shoulders 18 so that the cutting portion 11 swings away from the tunnel wall or floor 19 in the direction of arrow T in FIG. 1. This feature permits control of the direction of advancement of the shield shown in FIGS. 4 and 5 as will now be described but it should be mentioned that it is possible to achieve the same effect by utilizing wedges or spindles or the like instead of the units 13 to displace the component 22. Referring back to FIGS. 4 and 5 it has been described how the shield is advanced by using the frames 30, 31 but now it will be appreciated that the members M over the floor 19 of the tunnel are constructed as shown in FIGS. 1 to 3. The components 22 of the members M normally engage on the floor 19 as shown in FIG. 5 with the units 13 extended as shown in FIG. 1. If during the course of advancement of the shield the shield overall tends to become displaced towards the floor 19 so that the tunnel drifts towards the floor the units 13 of the members M can be retracted as represented in FIG. 3. In this way the tapered clearance 28 of FIG. 3 is established between the component 22 of each member M and the floor 19' as represented in FIG. 5. Each of the members M can now tilt about its fulcrum 29 on the floor 19 to bring its forward portion away from the floor 19'. This tilting occurs due to the fact that the majority of the weight of the shield acts on the members M and also because of the forces acting on the moving frame 30, 31 as the members M' are'advanced thereby. The result of this tilting is for the entire shield to tend to rise away from the floor as the members M, M are advanced. In this way by adjusting the units 13 the shield can be steered to control the direction of the tunnelling progress.

The special members M are most effective over the floor region of the tunnel although it is possible to provide such members in other locations such as the sides or roof in addition or alternatively to the floor region. Individual members M can be positioned between the ordinary members M as represented by the reference M" in FIG. 4. The action of the members M in all cases is the same and it can be appreciated that it is possible to control the direction of advancement of the tunnel from a number of aspects more usually laterally and vertically.

Iclaim:

1. An advanceable shield for a tunnelling machine, said shield comprising: a plurality of individual longitudinally displaceable elongate members arranged sideby-side and disposed generally around the longitudinal axis of a tunnel, said elongate members contacting and supporting the tunnel wall to define a excavation space, means for supporting and guiding all said elongate members during longitudinal movement, means for selectively shifting one or more of said elongate members at a time in the longitudinal direction of tunnel advance, at least one of said elongate members having a main body, a further component displaceably attached to said main body, and means for selectively displacing said further component generally transversally of the longitudinal axis of said main body, said selective displacing means operably controlling the direction of tunnel advancement.

2. An advanceable shield for a tunnelling machine, said shield comprising: a plurality of individual longitudinally displaceable elongate members arranged sideby-side and disposed generally around the longitudinal axis of a tunnel, said elongate members contacting and supporting the tunnel wall to define an excavation space, means for supporting and guiding all said elongate members during longitudinal movement, means for selectively shifting one or more of said elongate members at a time in the direction of tunnel advance, at least one of said members having a main body, a further component, means for pivotally connecting said further component to said main body, and means for pivotally displacing said further component upwardly or downwardly with relation to a plane containing an external surface of said main body, said further component engaging the tunnel wall, said pivotal displacement means operably controlling the direction of tunnel advancement.

3. A shield according to claim 1, wherein said selective displacing means is a piston and cylinder unit.

4. A shield according to claim 2, wherein said pivotal displacement means is a piston and cylinder unit.

5. A shield according to claim 1, wherein said main body of said at least one elongate member is of elongate forrn having a cutting portion at the forward end thereof.

6. A shield according to claim 1, wherein said main body and said further component of said at least one elongate member are each of elongate form.

7. A shield according to claim 1, wherein said main body of said at least one elongate member is of hollow construction and said further component fits at least partly within said main body.

8. A shield according to claim 1, wherein said further component of said at least one elongate member is pivotally connected to said main body thereof.

9. A shield according to claim 8, wherein a first portion of the length of said main body of said at least one elongate member has an inverted substantially U- shaped cross-section, and said further component pivots within said first portion of the length of said main body.

10. A shield according to claim 9, wherein said first portion of said main body of said at least one elongate member adjoins a second portion of said main body, said second portion having a rectangular cross-section, said second portion mounting a cutting portion at its forward end.

11. A shield according to claim 9, wherein said first portion of said main body of said at least one elongate member has side walls and a top wall defining the inverted substantially U-shaped cross-section, each of said side walls being tapered to decrease its vertical dimension towards the rearward end of said main body.

12. A shield according to claim 11, wherein said further component of said at least one elongate member has side walls and a bottom wall defining a generally U- shaped cross-section, said further component bottom wall facing said first portion top wall, each of said side walls of said further component being tapered to decrease its vertical dimension towards the rearward end of said main body, and wherein said further component is pivotally attached to said main body by pivot pins extending through said side walls of said first portion of said main body and through said further component and projecting inwardly thereof.

13. A shield according to claim 10, wherein said first portion of said main body of said at least one elongate member has side walls and a top wall defining the inverted substantially U-shaped cross-section, each of said side walls being tapered to decrease its vertical dimension towards the rearward end of said main body, said second portion has side walls continuous with said side walls of said first portion, a top wall continuous with said top wall of said first portion, and a bottom wall parallel to said top wall of said first portion, said second portion bottom wall terminates at the juncture between said first portion and said second portion, and wherein a shoulder is formed at the junction of said side walls of said first portion and said second portion.

14. A shield according to claim 12, wherein said main body and said further component of said at least one elongate member are each provided with reinforcement webs.

15. A shield according to claim 13, wherein said further component of said at least one elongate member is generally of U-shaped cross-section having side walls and a bottom wall disposed to face said top walls of said first and second portions of said main body, said side walls of said further component being tapered to decrease its vertical dimension towards the rearward end of said first portion of said main body.

16. A shield according to claim 15, wherein said further component is adjustable by said selective displacing means between a first position wherein said further component bottom wall is co-planar with said bottom wall of said second portion of said main body, and a second position wherein said further component bottom wall is disposed vertically above a plane containing said bottom wall of said second portion.

17. A shield according to claim 1, wherein each said elongate member has a cutting portion at its forward end.

18. A shield according to claim 1, wherein said means for supporting said elongate members includes at least one frame.

19. A shield according to claim 1, wherein said means for supporting said elongate members comprises two frame.

20. A shield according to claim 1, wherein said means for supporting said elongate members comprises two frames, there being further provided means for selectively locking each of said elongate members to at least one of said frames, and ram means for shifting one or more of said elongate members to effect relative displacement between said frames.

21. A shield according to claim 1, said shield including a group comprising a plurality of said elongate members, each said elongate member in said group having a main body and a further component and a selective displacing means, said group of elongate members being located at least partially adjacent to the floor of the tunnel.

22. A shield according to claim 21, wherein said main body of each of said elongate members of said group has a rearward end portion having side walls and a top wall defining an inverted substantially U-shaped crosssection, said side walls tapering to decrease their vertical dimension towards the rearward end of said elongate member, wherein said further component of each of said elongate members of said group has side walls and a bottom wall defining a substantially U-shaped cross-section, said side walls tapering to decrease their vertical dimension towards the rearward end of said elongate member, wherein said main portion top wall faces said further component bottom wall, wherein said further component is pivotally connected to said main body to pivot between an upper position wherein said further component is disposed substantially within said rearward end of said main body, and a lower position wherein said bottom wall of said further component is co-planar with said bottom wall of said second portion of said main body.

23. A shield according to claim 22, wherein said main body of each of said elongate members of said group has a forward end portion having side walls continuous with said side walls of said rearward end portion thereof, and having a bottom wall for contacting the tunnel wall, the tapered lower edges of said side walls of said rearward end portion of said main body of each of said elongate members of said group terminating in shoulders at their junction with said side walls of said forward end portion, the shoulders adjoining the rearward end of said bottom wall of said forward end portion and forming therewith a support surface about which said elongate member is tiltable in dependence on the operation of said selective displacing means to effect control of the direction of the tunnel advancement.

24. A shield according to claim 19, wherein said selective shifting means comprises means for selectively locking each said elongate member to at least one of said frames, and means for relatively displacing said frames in the direction of tunnel advancement. 

1. An advanceable shield for a tunnelling machine, said shield comprising: a plurality of individual longitudinally displaceable elongate members arranged side-by-side and disposed generally around the longitudinal axis of a tunnel, said elongate members contacting and supporting the tunnel wall to define a excavation space, means for supporting and guiding all said elongate members during longitudinal movement, means for selectively shifting one or more of said elongate members at a time in the longitudinal direction of tunnel advance, at least one of said elongate members having a main body, a further component displaceably attached to said main body, and means for selectively displacing said further component generally transversally of the longitudinal axis of said main body, said selective displacing means operably controlling the direction of tunnel advancement.
 2. An advanceable shield for a tunnelling machine, said shield comprising: a plurality of individual longitudinally displaceable elongate members arranged side-by-side and disposed generally around the longitudinal axis of a tunnel, said elongate members contacting and supporting the tunnel wall to define an excavation space, means for supporting and guiding all said elongate members during longitudinal movement, means for selectively shifting one or more of said elongate members at a time in the direction of tunnel advance, at least one of said members having a main body, a further component, means for pivotally connecting said further component to said main body, and means for pivotally displacing said further component upwardly or downwardly with relation to a plane containing an external surface of said main body, said further component engaging the tunnel wall, said pivotal displacement means operably controlling the direction of tunnel advancement.
 3. A shield according to claim 1, wherein said selective displacing means is a piston and cylinder unit.
 4. A shield according to claim 2, wherein said pivotal displacement means is a piston and cylinder unit.
 5. A shield according to claim 1, wherein said main body of said at least one elongate member is of elongate form having a cutting portion at the forward end thereof.
 6. A shield according to clAim 1, wherein said main body and said further component of said at least one elongate member are each of elongate form.
 7. A shield according to claim 1, wherein said main body of said at least one elongate member is of hollow construction and said further component fits at least partly within said main body.
 8. A shield according to claim 1, wherein said further component of said at least one elongate member is pivotally connected to said main body thereof.
 9. A shield according to claim 8, wherein a first portion of the length of said main body of said at least one elongate member has an inverted substantially U-shaped cross-section, and said further component pivots within said first portion of the length of said main body.
 10. A shield according to claim 9, wherein said first portion of said main body of said at least one elongate member adjoins a second portion of said main body, said second portion having a rectangular cross-section, said second portion mounting a cutting portion at its forward end.
 11. A shield according to claim 9, wherein said first portion of said main body of said at least one elongate member has side walls and a top wall defining the inverted substantially U-shaped cross-section, each of said side walls being tapered to decrease its vertical dimension towards the rearward end of said main body.
 12. A shield according to claim 11, wherein said further component of said at least one elongate member has side walls and a bottom wall defining a generally U-shaped cross-section, said further component bottom wall facing said first portion top wall, each of said side walls of said further component being tapered to decrease its vertical dimension towards the rearward end of said main body, and wherein said further component is pivotally attached to said main body by pivot pins extending through said side walls of said first portion of said main body and through said further component and projecting inwardly thereof.
 13. A shield according to claim 10, wherein said first portion of said main body of said at least one elongate member has side walls and a top wall defining the inverted substantially U-shaped cross-section, each of said side walls being tapered to decrease its vertical dimension towards the rearward end of said main body, said second portion has side walls continuous with said side walls of said first portion, a top wall continuous with said top wall of said first portion, and a bottom wall parallel to said top wall of said first portion, said second portion bottom wall terminates at the juncture between said first portion and said second portion, and wherein a shoulder is formed at the junction of said side walls of said first portion and said second portion.
 14. A shield according to claim 12, wherein said main body and said further component of said at least one elongate member are each provided with reinforcement webs.
 15. A shield according to claim 13, wherein said further component of said at least one elongate member is generally of U-shaped cross-section having side walls and a bottom wall disposed to face said top walls of said first and second portions of said main body, said side walls of said further component being tapered to decrease its vertical dimension towards the rearward end of said first portion of said main body.
 16. A shield according to claim 15, wherein said further component is adjustable by said selective displacing means between a first position wherein said further component bottom wall is co-planar with said bottom wall of said second portion of said main body, and a second position wherein said further component bottom wall is disposed vertically above a plane containing said bottom wall of said second portion.
 17. A shield according to claim 1, wherein each said elongate member has a cutting portion at its forward end.
 18. A shield according to claim 1, wherein said means for supporting said elongate members includes at least one frame.
 19. A shield according to claim 1, wherein said means for supporting said elongate members comprises two frame.
 20. A shield according to claim 1, wherein said means for supporting said elongate members comprises two frames, there being further provided means for selectively locking each of said elongate members to at least one of said frames, and ram means for shifting one or more of said elongate members to effect relative displacement between said frames.
 21. A shield according to claim 1, said shield including a group comprising a plurality of said elongate members, each said elongate member in said group having a main body and a further component and a selective displacing means, said group of elongate members being located at least partially adjacent to the floor of the tunnel.
 22. A shield according to claim 21, wherein said main body of each of said elongate members of said group has a rearward end portion having side walls and a top wall defining an inverted substantially U-shaped cross-section, said side walls tapering to decrease their vertical dimension towards the rearward end of said elongate member, wherein said further component of each of said elongate members of said group has side walls and a bottom wall defining a substantially U-shaped cross-section, said side walls tapering to decrease their vertical dimension towards the rearward end of said elongate member, wherein said main portion top wall faces said further component bottom wall, wherein said further component is pivotally connected to said main body to pivot between an upper position wherein said further component is disposed substantially within said rearward end of said main body, and a lower position wherein said bottom wall of said further component is co-planar with said bottom wall of said second portion of said main body.
 23. A shield according to claim 22, wherein said main body of each of said elongate members of said group has a forward end portion having side walls continuous with said side walls of said rearward end portion thereof, and having a bottom wall for contacting the tunnel wall, the tapered lower edges of said side walls of said rearward end portion of said main body of each of said elongate members of said group terminating in shoulders at their junction with said side walls of said forward end portion, the shoulders adjoining the rearward end of said bottom wall of said forward end portion and forming therewith a support surface about which said elongate member is tiltable in dependence on the operation of said selective displacing means to effect control of the direction of the tunnel advancement.
 24. A shield according to claim 19, wherein said selective shifting means comprises means for selectively locking each said elongate member to at least one of said frames, and means for relatively displacing said frames in the direction of tunnel advancement. 